Preparation of Half-Sandwich Osmium Complexes by Deprotonation of Aromatic and Pro-aromatic Acids with a Hexahydride Brønsted Base

Esteruelas, Miguel A.; García-Raboso, Jorge; Oliván, Montserrat

doi:10.1021/om200371r

Cited by 27 publications

(20 citation statements)

References 89 publications

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“…Figure 2 shows a view of the molecule. The structure with Cs symmetry resembles those of complexes OsH 3 X(PR 3 ) 2 (PR 3 = P t Bu 2 Me, and X = Cl; PR 3 = P i Pr 3 , and X = Cl, Br, or I), 21 OsH 3 (OR f )(P i Pr 3 ) 2 [OR f = OCH 2 CF 3 or OCH(CF 3 ) 2 ], 22 OsH 3 (OPh)(P i Pr 3 ) 2 , 23 OsH 3 Cl(IPr)(P i Pr 3 ) [IPr = 1,3-bis-(diisopropylphenyl)imidazolylidene], 24 and OsH(Bcat) 2 Cl-(P i Pr 3 ) 2 (Bcat = catecholboryl). 25 The phosphines are disposed mutually trans [P(1)−Os−P(2), 170.62(3)°], whereas the hydrides and azavinylidene lie in the plane perpendicular to the P−Os−P direction.…”

Section: ■ Results and Discussionmentioning

confidence: 92%

Reduction of Benzonitriles via Osmium–Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers

et al. 2019

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The reduction of the N-C triple bond of benzonitriles promoted by OsH6(P i Pr3)2 (1) has been studied. Complex 1 releases a H2 molecule and coordinates 2,6-dimethylbenzonitrile to afford the tetrahydride OsH4{κ 1-N-(NCC6H3Me2)}(P i Pr3)2 (2), which is thermally stable towards the insertion of the nitrile into one of the Os-H bonds. In contrast to 2,6-dimethylbenzonitrile, benzonitrile and 2-methylbenzonitrile undergo insertion, via Os(η 2-NCR) intermediates, to give the azavinylidene derivatives OsH3(=N=CC6H4R)(P i Pr3)2 (R = H (3), Me (4)). The analysis by means of computational tools (EDA-NOCV) of the bonding situation in these compounds suggests that the donor-acceptor nature of the osmium azavinylidene bond dominates over the mixed electron-sharing/donor-acceptor and pure electron-sharing bonding modes. The N atom is strongly nucleophilic whereas one of the hydrides is electrophilic. In spite of the different nature of these centers, the migration of the latter to the N atom is kinetically prevented. However, the use of water as a proton shuttle allows the hydride migration, as a consequence of a significant decrease of the activation barrier. The resulting phenylaldimine intermediates evolve by means of orthometalation to give OsH3{κ 2-N,C-(NH=CHC6H3R)}(P i Pr3)2 (R = H (5), Me (6)). The presence of electrophilic and nucleophilic centers in 3 confers it ability to activate σ-bonds, including H2 and pinacolborane (HBpin). The reaction with the latter gives OsH3{κ 2-N,C-[N(Bpin)=CHC6H4]}(P i Pr3)2 (7). Supporting Information. The following files are available free of charge. General information, crystallographic data, computational details, NMR and IR spectra (PDF) Cartesian coordinates of calculated structures (XYZ) Accession Codes CCDC 1907065-1907067 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_

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Section: ■ Results and Discussionmentioning

confidence: 92%

Reduction of Benzonitriles via Osmium–Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers

et al. 2019

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“…Polyhydrides of platinum group metals are a class of transition-metal compounds, which have the ability of activating σ-bonds . In particular, the d 2 -hexahydride complex 1 has proved to promote the rupture of C–H, C–C, C–N, O–H, and N–H bonds. In agreement with this, the treatment of 2-propanol solutions of this polyhydride with 1.0 equiv of HBMePI, under reflux, for 6 h leads to the trihydride-osmium(IV) derivative OsH 3 {κ 2 -N py ,N imine -(BMePI)}(P i Pr 3 ) 2 , as a result of the deprotonation of the polycycle, by action of a hydride ligand, and the coordination of a pyridyl group and its adjacent imine function of the resulting anion.…”

Section: Resultsmentioning

confidence: 99%

Osmium Catalysts for Acceptorless and Base-Free Dehydrogenation of Alcohols and Amines: Unusual Coordination Modes of a BPI Anion

et al. 2018

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A novel type of catalyst precursors for the dehydrogenation of hydrogen carriers based on organic liquids has been discovered. Complexes OsH6(P i Pr3)2 (1) and OsH(OH)(CO)(P i Pr3)2 (2) react with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePI) to give OsH3{κ 2-Npy,Nimine-(BMePI)}(P i Pr3)2 (3) and OsH{κ 2-Npy,Nimine-(BMePI)}(CO)(P i Pr3)2 (4). The unprecedented  2-Npy,Nimine coordination mode of BMePI is thermodynamically preferred with Os(IV) and Os(II) metal fragments and allows to prepare BMePI-based dinuclear metal cations. Treatment of OsH2Cl2(P i Pr3)2 (5) with 0.5 equiv of HBMePI in the presence of KO t Bu affords the chloride salt of the bis(osmium(IV)) dinuclear cation [{OsH3(P i Pr3)2}2{-( 2-Npy,Nimine)2-BMePI}] + (6). Related homoleptic bis(osmium(II)) complexes have been also synthetized. Complex 4 reacts with the bis(solvento) [OsH(CO){ 1-O-[OCMe2]2}(P i Pr3)2]BF4 to give [{OsH(CO)(P i Pr3)2}2{-( 2-Npy,Nimine)2-BMePI}]BF4 (7), whereas the addition of 0.5 equiv of HBMePI to {OsCl( 6-C6H6)}2(-Cl)2 (8) affords [{OsCl( 6-C6H6)}2{-(κ 2-Npy,Nimine)2-BMePI}]Cl (9). The reactions of 4 with 8 and {OsCl( 6-p-cymene)}2(-Cl)2 (10) lead to the heteroleptic cations [(P i Pr3)2(CO)HOs{-( 2-Npy,Nimine)2-BMePI}OsCl( 6-arene)] + (arene = C6H6 (11), p-cymene (12)). The electronic structrure and electrochemical properties of the dinuclear complexes were also studied. Complexes 3 and 4 are efficient catalyst precursors for the acceptorless and base-free dehydrogenation of secondary and primary alcohols and cyclic and lineal amines. The primary alcohols afford aldehydes. The amount of H2 released per gram of heterocycle depends upon: the presence of a methyl group adjacent to the nitrogen atom, the position of the nitrogen atom in the heterocycle, and the size of the heterocycle.

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“…The hydride ligands of the d 2 hexahydride complex 1 have proved to be basic enough to promote the deprotonation of polar C–H, N–H, and O–H σ-bonds. In agreement with this, treatment of toluene solutions of 1 with 2 equiv of Hacac, under reflux, for 1 h leads to the trihydride derivative OsH 3 (acac)(P i Pr 3 ) 2 ( 3 ) and H 2 (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

Osmium Hydride Acetylacetonate Complexes and Their Application in Acceptorless Dehydrogenative Coupling of Alcohols and Amines and for the Dehydrogenation of Cyclic Amines

et al. 2017

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The preparation of new osmium-hydride complexes, starting from OsH 6 (P i Pr 3) 2 (1) and OsH 2 Cl 2 (P i Pr 3) 2 (2), and their catalytic activity in acceptorless dehydrogenative coupling of alcohols and amines and in dehydrogenation of cyclic amines are reported. Complex 1 reacts with acetylacetone (Hacac) to give the classical trihydride OsH 3 (acac)(P i Pr 3) 2 (3). The protonation of 3 with triflic acid (HOTf) produces the release of H 2 and the formation of the unsaturated osmium(IV)-dihydride [OsH 2 (acac)(P i Pr 3) 2 ]OTf (4), which is also prepared starting from 2 via the intermediate OsH 2 Cl(acac)(P i Pr 3) 2 (5). Treatment of acetylacetone solutions of 5 with KOH affords Os(acac) 2 (P i Pr 3) 2 (6). In presence of 5 mol% of KOH, complexes 3-6 promote the coupling of benzylalcohol and aniline to give N-benzylideneaniline and H 2. Under the same conditions, complex 3 catalyzes a wide range of analogous couplings to afford a variety of imines, including aliphatic ones, with yields between 90 and 40% after 1-48 h. Complex 3 also catalyzes the dehydrogenation of cyclic amines. According to the amount of H 2 released by each gram of employed substrate, the amines have been classified into three classes: poor-(1,2,3,4-tetrahydroquinaldine, 2-methylindoline and 2,6dimethylpiperidine), moderate-(1,2,3,4-tetrahydroquinoline and 6-methyl-1,2,3,4-tetrahydroquinoline) and good-hydrogen donors (1,2,3,4-tetrahydroisoquinoline).

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Preparation of Half-Sandwich Osmium Complexes by Deprotonation of Aromatic and Pro-aromatic Acids with a Hexahydride Brønsted Base

Cited by 27 publications

References 89 publications

Reduction of Benzonitriles via Osmium–Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers

Reduction of Benzonitriles via Osmium–Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers

Osmium Catalysts for Acceptorless and Base-Free Dehydrogenation of Alcohols and Amines: Unusual Coordination Modes of a BPI Anion

Osmium Hydride Acetylacetonate Complexes and Their Application in Acceptorless Dehydrogenative Coupling of Alcohols and Amines and for the Dehydrogenation of Cyclic Amines

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